Abstract
The progesterone level in the peripheral blood serum of 5 mares was determined by radioimmunoassay during the estrous cycle and gestation period.
Material and method: The 5 mares used in this study were 2 Percherons and 3 Bretons of the Tokachi Livestock-Breeding Station, Hokkaido. Sexual receptivity of them was checked every 2 to 3 days by a teaser stallion, and the internal genitalia was examined by rectum palpation. The blood samples were collected from jugular vein of the mares at intervals of 1 to 2 days during the follicular phase, and of 2 to 3 days during the luteal phase, further of 15 or 30 days during the gestation period. Serum samples (0.0250.2 ml) were extracted with ethyl ether, and assayed by the radioimmunoassay technique of MAKINe4. The assay water blank showed 00.013 ng, and the recovery rate was 75100 percent. The working range of the standard curve was from 0 to 1 ng of progesterone.
Result: Throughout the estrous cycle in non-pregnant mares the progesterone levels showed the lowest just at estrus (1.039, with a range of 0.3891.363 ng/ml at day of ovulation), and on the 5th day it commenced to rise. Thereafter, the increased value reached a peak of 9.454 (5.36114.961)ng/ml on the 10th day, then dropped rapidly towards the 20th day.
In pregnancy, progesterone on the 15th day had a mean value of 13.008 (7.00518.961) ng/ ml, higher than that on the 20th day (mean of 5.857, range 3.176 to 10.897 ng/ml). Between the 30th and the 105th day there was an indication of increase on progesterone levels. There-after, it commenced to drop rapidly to 6.350 (5.1287.573) ng/ml at the 120th day. A rise was observed in progesterone levels in these 5 mares, after each 150th day of gestation.
The highest mean level among the 5 mares was 22.548 (10.71641.080) ng/ml which obtained from the sample at each 225th day of gestation. However, after the 240th day these levels declined gradually.
The present report indicates that the plasma progesterone level assayed could be useful for pregnancy diagnosis in early gestation and also for judging the fetal well-being status during pregnancy.
